linux-kernel - Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl

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Message-ID: <e02c727a-5505-80d3-9ba2-9fbb9c8253fe@huawei.com>
Date:   Tue, 10 Sep 2019 13:34:59 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Scott Wood <oss@...error.net>, <mpe@...erman.id.au>,
        <linuxppc-dev@...ts.ozlabs.org>, <diana.craciun@....com>,
        <christophe.leroy@....fr>, <benh@...nel.crashing.org>,
        <paulus@...ba.org>, <npiggin@...il.com>, <keescook@...omium.org>,
        <kernel-hardening@...ts.openwall.com>
CC:     <wangkefeng.wang@...wei.com>, <linux-kernel@...r.kernel.org>,
        <jingxiangfeng@...wei.com>, <zhaohongjiang@...wei.com>,
        <thunder.leizhen@...wei.com>, <fanchengyang@...wei.com>,
        <yebin10@...wei.com>
Subject: Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32

Hi Scott,

On 2019/8/28 12:05, Scott Wood wrote:
> On Fri, 2019-08-09 at 18:07 +0800, Jason Yan wrote:
>> This series implements KASLR for powerpc/fsl_booke/32, as a security
>> feature that deters exploit attempts relying on knowledge of the location
>> of kernel internals.
>>
>> Since CONFIG_RELOCATABLE has already supported, what we need to do is
>> map or copy kernel to a proper place and relocate.
> 
> Have you tested this with a kernel that was loaded at a non-zero address?  I
> tried loading a kernel at 0x04000000 (by changing the address in the uImage,
> and setting bootm_low to 04000000 in U-Boot), and it works without
> CONFIG_RANDOMIZE and fails with.
> 

How did you change the load address of the uImage, by changing the
kernel config CONFIG_PHYSICAL_START or the "-a/-e" parameter of mkimage?
I tried both, but it did not work with or without CONFIG_RANDOMIZE.


Thanks,
Jason

>>   Freescale Book-E
>> parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
>> entries are not suitable to map the kernel directly in a randomized
>> region, so we chose to copy the kernel to a proper place and restart to
>> relocate.
>>
>> Entropy is derived from the banner and timer base, which will change every
>> build and boot. This not so much safe so additionally the bootloader may
>> pass entropy via the /chosen/kaslr-seed node in device tree.
> 
> How complicated would it be to directly access the HW RNG (if present) that
> early in the boot?  It'd be nice if a U-Boot update weren't required (and
> particularly concerning that KASLR would appear to work without a U-Boot
> update, but without decent entropy).
> 
> -Scott
> 
> 
> 
> .
>